Excerpt:
The original isotope ratio method for detecting C-4 (com and cane) sugars in honey was qualified by AOAC in 1977. The wide range of values found for pure honeys made it necessary to use a statistical approach in setting limits for pure honey. A range of -23.5°/00 to -21.5°100 was set for questionable samples; honeys more negative than -23.5°/00 were considered pure and samples less negative than -21.5°/00 were considered adulterated without further testing. Those between these two limits would require further testing by the TLC test. This test has several shortcomings: it requires visual judgement of colors and intensities, does not include cane sugar, and is somewhat vulnerable to newer improved high-fructose com syrups. The ISCIRA (internal standard) test was developed in the late 1980’s and accepted by AOAC in 1991 to eliminate the ambiguous TLC test, though it was realized (and so stated in the AOAC method description) that it is valid for honeys of any isotope ratio value.
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